[RESOLVED] Subtle differences in std::vector

[dude_1967]

Hello,

I am studying subtle differences in the implementation of std::vector<T> for Microsoft and GCC compilers.

The program shown below gives different output for the two compilers. You need to look in the comments to see the outputs. I perfectly understand the output from GCC.

Output from GCC does this:
- CTOR 1: Creates one dummy on the stack for the vector's ctor
- Uses this dummy to initialize the vector
- DTOR 1: Deletes this dummy off the stack when vector's ctor is done.
- DTOR 2-3: vector's clear function deletes two dummys.

However, I don't understand why the Microsoft compiler has different output. I perused ISO/IEC 14882:2003 but could not find these implementation details.
- Shouldn't this stuff be specified?
- Why do these compilers seem to have implementation freedom?

#include <vector>
#include <iostream>

struct dummy
{
  static unsigned ctor_count;
  static unsigned dtor_count;

  dummy()
  {
    ++ctor_count;
    std::cout << "C-TOR of dummy" << std::endl;
  }

  ~dummy(void)
  {
    ++dtor_count;
    std::cout << "D-TOR of dummy" << std::endl;
  }
};

unsigned dummy::ctor_count;
unsigned dummy::dtor_count;

int main(void)
{
  std::vector<dummy> vd(2u);
  vd.clear();

  std::cout << "JUST AFTER CLEAR!" << std::endl;

  std::cout << "Number of dummy ctors: " << dummy::ctor_count << std::endl;
  std::cout << "Number of dummy dtors: " << dummy::dtor_count << std::endl;
}

/*
Visual Studio 2010
------------------
C-TOR of dummy
D-TOR of dummy
C-TOR of dummy
D-TOR of dummy
D-TOR of dummy
D-TOR of dummy
JUST AFTER CLEAR!
Number of dummy ctors: 2
Number of dummy dtors: 4
*/

/*
GCC 4.5.2
$ g++ -Wall -Wextra -pedantic -std=c++0x -O3 test.cpp -o test.exe
------------------
C-TOR of dummy
D-TOR of dummy
D-TOR of dummy
D-TOR of dummy
JUST AFTER CLEAR!
Number of dummy ctors: 1
Number of dummy dtors: 3
*/